A nuclease from a marine bacterium of genus Alteromonas is to be further characterized with respect to physical and kinetic properties and its detailed mechanism of action upon various DNA substrates. Two kinetically distinct forms of the enzyme, arising depending upon the purification procedure used, will be characterized as to the kinetic parameters for the random hydrolysis of single-stranded DNA and those for the terminally directed hydrolysis of duplex DNA. The mechanism of action for the shortening of linear duplex DNA from the termini will be investigated and the extent to which nucleotide removal is processive will be determined. A possible method for blocking the duplex exonuclease activity, very desirable in some connections, will be tested. The mechanism by which the Alteromonas nuclease cleaves both strands of supercoiled closed circular duplexes and at the sites of single-strand breaks (nicks) in duplex DNA substrates will be examined. The ribonuclease activity associated with the enzyme will be examined through its activity upon duplex RNA substrates. If terminally directed hydrolysis against duplex RNAs, without concomitant introduction of scissions away from the termini, is observed, the kinetics of this activity will be determined. Ongoing studies in which the Alteromonas nuclease is used to detect very low levels of covalent modification in duplex DNA caused by carcinogenic or mutagenic agents will be extended.